Sandwich materials, which consist of different materials, combine contradictory properties which cannot be provided by monolithic materials. Thus, for example, a sandwich material consisting of a plastic core layer with two metallic cover layers, particularly when the plastic core layer is provided with a thickness which is greater than the thickness of the metal cover layers, has comparable properties to a monolithic material, with a reduced weight. On account of the plastic core layer arranged between the metal cover layers and separating the two metal cover layers from one another in an insulating manner, the resistance spot welding of a sandwich material with at least one further metallic material was to date very difficult and could only be carried out with a high outlay on apparatus. Resistance spot welding methods of the generic type are known from the prior art.
The German laid-open specification DE 10 2011 109 708 A1 discloses a method for the resistance spot welding of a sandwich component with a further metal component, in which a first electrode is placed onto the surface of the metal component and a second electrode is placed in an opposing manner onto the surface of the sandwich component at the site to be welded, and the plastic at the site to be welded is heated, wherein the temperature of the electrodes is controlled, and, by moving the electrodes together, the softened plastic is displaced out of the region to be welded until the cover layers of the sandwich component come into electrical contact. By the application of an electrical current across the two electrodes, a welded connection is formed between the cover layers of the sandwich component and the metal component. It is disadvantageous here that the method has very high processing times and the corresponding device has a very complex structure.
The German patent application DE 10 2013 108 563 A1 discloses a method for the resistance spot welding of a sandwich component with a metal component, in which a second electric circuit is used between two electrodes for welding the sandwich component with the metal component. The plastic is heated at the site to be welded by a first electric circuit, which is energized by way of the same current/voltage source as the second electric circuit and is shiftable or disengageable. The current for heating energizes the electrode which lies against the surface of the metal component, and conducts the current into the metal component. The current is fed back to the current/voltage source by a current bridge arranged in electrical contact with the metal component. The distance or the path between the feeding electrode and the power-tapping current bridge can be chosen to be too great, as a result of which the heat introduced over this distance can have a negative effect in the sandwich material; by way of example, delamination can occur in this region. There is therefore further potential for improvement.